Protein requirements of lactating dairy cows have been investigated with and without additions of methionine to the diet. Two groups of 12 Holstein cows were individually fed either 80% or 100% of the recommended crude protein requirement. Each cow received either the basal ration, basal ration plus 21 grams per day methionine, or basal ration plus grams per day methionine-hydroxyanalog (MHA) in the balanced incomplete block switchback design. Supplemental MHA did not significantly affect any measurement of cow productivity nor did underfeeding crude protein significantly reduce production (28.5 versus 30.1 kilograms per day). The effects of postruminal infusion of amino acids on milk production and milk composition were investigated using 5 rumen fistulated cows in a 5 by 5 Latin Square design. The 5 treatments consisted of postruminal infusion of water, casein, essential (EAA) plus nonessential amino acids (NEAA), EAA, and NEAA. Cows receiving abomasal infusions of casein, EAA plus NEAA, or EAA produced .7 to .9 kilograms more milk and 80 to 130 grams more milk protein/cow/day than cows infused with water. Various methods of evaluating amino acid requirements suggest methionine, lysine, and phenylalanine to be potentially limiting amino acids for milk and milk protein production. Both in vitro and in vivo studies have been conducted to investigate the effects of ammonia on glucose metabolism. Addition of ammonia to liver tissue slice incubations or intraruminal administration of .4 grams of urea per kilogram of body weight in four daily steers altered glucose production and utilization. The practical significance between the observed effects of ammonia on glucose metabolism and utilization of urea in feeds by ruminants remains speculative. However, it is possible that feeding practices which increase the efficiency of urea utilization may do so, partially, by minimizing deterimental effects on glucose metabolism.